This invention relates to an improved guide means surface in the travelling path of a magnetic tape.
"Travelling path" as used in this invention is formed by guide means such as guide pins, guide rolls, tension rolls, and guide plates so that magnetic tape can be transported continuously in a given direction in an audio or video record/reproduce system, dubbing system, or tape takeup system in tape processing steps.
The recent development of high-performance audio and video record/reproduce systems has enabled many continuous hours or recording/reproducing operation, and the record/reproduce period, which originally had been only 2 hours with Betamax or VHS video tape cassette recording systems, has now been extended to as long as 6 hours, and is expected to be extended up to 9 hours in the near future.
To achieve such extended recording and reproduction, a magnetic tape with increased effective recording area is necessary. To meet this requirement, two methods have been proposed: one method is to reduce the thickness of the magnetic tape, to thereby increase the length of the tape that can be stored in a given space; and the other method is to provide increased recording density by reducing the width of tracks travelled by the magnetic head or by slowing the tape transport speed. But to increase the effective recording area of the magnetic tape, several problems must be solved, such as low mechanical strength and poor physical characteristics due to a thin thickness of the tape, a low electromagnetic conversion efficiency, and a narrow permissible range of dropouts due to the change in the width of tracks or tape speed.
Conventional means to solve these problems include using tape guide means wherein the surface that contacts the magnetic tape is made as smooth as possible to prevent the development of abrasions on the tape surface, increasing the surface hardness of the tape contact face to minimize shaving or wear caused by abrasion of the magnetic tape, and using a material having low affinity with the magnetic tape. However, the surface characteristics of the magnetic tape to be guided, particularly, its surface roughness, hardness, lubricity, and antistatic properties, vary considerably from one type of tape to another, so tape cassette manufacturers have found it necessary to use guide means that are best suited to the specific type of magnetic tape expected to be used therewith, with the result that parts control becomes complicated and the manufacturing cost increases. Another problem with the ability of a particular guide means to guide only one type of tape is that it is very difficult to use more than one type of magnetic tape on the same record/reproduce system.
A further defect of the conventional tape guide means is described by reference to accompanying FIGS. 1 and 2, which show a conventional guide pin 1, or one kind of nonmagnetic cylindrical guide means, that forms part of a magnetic tape T path. Conventionally, guide pin 1 is a cylindrical member made of nonmagnetic stainless steel or a plastic resin impregnated with silicone. The outer peripheral surface of the member is finished to a surface roughness of about 0.2 S to 0.8 S (0.2 to 0.5 .mu.m) by barrel finishing, centerless grinding, superfinishing, vanishing or other finishing techniques. FIG. 2 is an enlarged schematic representation of the surfaces of such a conventional guide pin 1 in contact with a magnetic tape T. As shown, the surface S of the guide pin has a cross section with sharp sawteeth, and the ridges of the sawteeth produce abrasions on the surface S of the tape T that cause dropouts. To provide flat ridges by further grinding not only results in high processing costs but it often causes uneven running of the magnetic tape T because the tape sticks or adheres to the flat ridges. A plastic guide pin is not capable of retaining the desired surface roughness for an extended period because its surface is shaven by the abrasion of the magnetic tape, partly due to its low surface hardness, and the shavings therefrom are transferred onto the tape T to induce dropouts.